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325mm vented front brakes

This is a great upgrade for all Z4: you'll have the same front brakes as the 3.0si so I'll recommend upgrading the rear to 294mm. You will need 17" to clear the calipers.
You'll need the whole front caliper assembly from one of the following car:

E46 330i All
Z4 3.0si (Roadster & Coupe)

If you wanna be a perfectionist: the protection plate behind the 325mm rotor is bigger than what the 300mm or 286mm have (these two setups have the same cover). The rotors should fit with no particular issue as the cover does not interfere with the rotor. The problem with replacing this covers is that the wheel hub has be removed (you need a 46mm socket and an impact wrench) make it impractical if you are sourcing the parts from a junkyard. My friend Ed has been able to fit 325mm on a 323i Touring (originally equipped with 286mm as some Z4s) and had no issue.
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320mm vented rear brakes

If you find a E46 330i, you might also want to consider a full brake setup off this car: it would give you 325mm in the front and 320mm in the rear and it would be a bolt on swap...
Alternatively, 320mm rear vented rotors can be sourced off of an X3 (any model, old or new). As noted below, the X3 might not be able to provide you a full front and rear swap: the front calipers are the same as the E46 330i, but the caliper carrier has a different p/n.
In summary, 320mm vented rear rotors can be sourced from the following cars:

E46 330i All
E83 X3 All

320mm can be used only with 325mm front as you don't want to have your rear rotors bigger than the front. Although many variables go into calcuutf8g brake bias, the disk size ratio of a 325mm front - 320mm rear conversion is similar to what the 3.0i has so it should be fine. However such a brake setup was never chosen by BMW as a setup for the any Roadster.

Another note regarding 320mm rear brakes. In this case too they have a different protection plate (as for the 325mm front rotors setup), and in this case it gets in the way of the bigger rotor. Once again, removing the plate is not as practical as you have to remove the parking brake assembly and likely the wheel hub. To fix the issue I would personally just bent the plate of the way... Sometimes I agree with the saying that "is something doesn't fit, your hammer ain't big enough"...
Πηγη: https://www.z4-forum.com/forum/viewt...hp?f=24&t=8399